DESCRIPTION (Adapted from the Applicant' s Abstract): The goal of this project is to elucidate the mechanisms of synaptic transmission using Drosophila genetics. The application has two aims. The first aim is to examine the role of exocyst, a protein complex essential for proper exocytosis and transport of vesicles. By using mutations in Dsec5, the Drosophila homolog of one of the exocyst proteins, the application seeks to understand the significance of exocyst for membrane trafficking in a multicellular organism. In particular, it seeks to determine whether the complex is needed for the development of a synapse and whether it is continuously required for synapse function. The second aim is to conduct a large-scale mutant screen for new genes that may be important for synaptic transmission. The investigator has developed a novel screen (using heterozygous flies with homozygous mutant eyes) in which strong candidates can be identified efficiently. These mutants will be categorized as to the nature of their defects, and those that appear to be most directly related to synaptic transmission will be characterized further. It is expected that the screen should uncover new proteins that influence the synapse and should also yield mutations in biochemically identified proteins for which little functional data are now available.